The present invention is related to providing a compressor control circuit, more particularly, providing a circuit for controlling a compressor having a brushless D.C. motor.
In general, it is known that a brushless D.C. motor has advantages; the superior control characteristics are the same as a D.C. motor, and the reduction of noise and power consumption are significant. Therefore, nowadays there is a tendency to adapt the brushless motor to home appliances, but the adaption has lagged behind in respect to the cost and the control techniques below, the satisfaction of users until now. Almost all home appliances are accustomed to being adapted for an A.C. motor. For example, an A.C. induction motor adapted to a compressor of a refrigerator always constitutes a two pole motor which is fixed at the synchronizing speed of around 3500 rpm under the application of an alternative current power having the frequency of 50 to 60 Hz. Therefore, the temperature adjustment in the chambers of the refrigerator is performed at an on-off interval period such that the operation of the compressor is repeatedly turned on and off with a sensor detecting the temperature in a freezing chamber.
But, the operation causes a refrigerator to have the temperature ripple (1.degree.-40.degree. C.). It shortens the storing time for keeping the freshness of refrigerated foodstuffs such as vegetables and fruits, etc. At the start of the operation shifted from the non-operation condition accompanying the on-off operation of the inductive motor, the rush current is relatively greater, thereby requiring a larger amount of consumption power. At this time, the winding current density is five times to ten times over that flowing at the normal operation period. It results in increasing the induction vibration and the electromagnetic noise between a rotator and a stator. Furthermore, the operation noises are more amplified at the band which is resonant with the mechanical inherent vibration frequency of the compressor. The induction motor has a greater induction loss. It causes higher winding heating than that of a D.C. motor to thereby raise the inner temperature of the compressor, thereby deteriorating the operation efficiency thereof and easily degenerating the substance of the compressor.
The compressor has disadvantages due to the property of the A.C. induction motor in that it is difficult to operate at a continuosly variable speed, the operation efficiency is relatively lower, the electromagnetic noise is greater, and the optimum operation range according to the load fluctuation is relatively narrower. Similarly, a compressor adapted to an air conditioner has the same problems.
The refrigerator adopted the same compressor has a relatively greater amount of load fluctuation over 100% at maximum related with the setting of an outside temperature and chamber temperature. It requires the optimum efficiency operation according to the load fluctuation ratio.
An object of the present invention is to provide a compressor control circuit including a brushless D.C. motor, for enabling the operation speed control of a compressor to lead to an ideal continuous operation according to the load fluctuation without intermittent on-off operation.
Another object of the present invention is to provide a compressor control circuit including a brushless D.C. motor of a high efficiency and low noise, further comprising a control apparatus for varying the operation speed of the brushless motor and an operation control circuit for optimizing the operation input of the brushless motor dependent upon load fluctuation to greatly reduce the consumption power.